A newborn is found to have hemolytic jaundice. Peripheral blood smear shows microspherocytes. The direct Coombs (DAT) test is positive. The mother's blood group is O Rh-positive, and the baby's is A Rh-positive. The most likely cause is:

• A Rh incompatibility (anti-D alloimmunization)
• B Hereditary spherocytosis (ANK1 mutation)
• C G6PD deficiency triggered by oxidative stress
• D ABO incompatibility with maternal anti-A IgG crossing the placenta ✓

Explanation

When the mother is group O and the infant is group A or B, naturally occurring maternal anti-A or anti-B IgG antibodies (formed without prior sensitization, unlike Rh) can cross the placenta and cause hemolysis in the newborn — this is ABO hemolytic disease of the newborn (HDN). The DAT is positive due to maternal IgG coating fetal RBCs. Microspherocytes result from partial phagocytosis of antibody-coated cells. Rh HDN requires prior sensitization and both mother and baby being Rh-discordant; this baby is Rh-positive like the mother, excluding Rh incompatibility.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.